SLUB: Extract dma_kmalloc_cache from get_cache.

The rarely used dma functionality in get_slab() makes the function too
complex. The compiler begins to spill variables from the working set onto
the stack. The created function is only used in extremely rare cases so make
sure that the compiler does not decide on its own to merge it back into
get_slab().

Signed-off-by: Christoph Lameter <clameter@sgi.com>

---
 mm/slub.c |   66 +++++++++++++++++++++++++++++++++-----------------------------
 1 file changed, 36 insertions(+), 30 deletions(-)

Index: linux-2.6.22-rc4-mm2/mm/slub.c
===================================================================
--- linux-2.6.22-rc4-mm2.orig/mm/slub.c	2007-06-18 15:35:58.000000000 -0700
+++ linux-2.6.22-rc4-mm2/mm/slub.c	2007-06-18 15:38:48.000000000 -0700
@@ -2220,10 +2220,6 @@ EXPORT_SYMBOL(kmem_cache_destroy);
 struct kmem_cache kmalloc_caches[KMALLOC_SHIFT_HIGH + 1] __cacheline_aligned;
 EXPORT_SYMBOL(kmalloc_caches);
 
-#ifdef CONFIG_ZONE_DMA
-static struct kmem_cache *kmalloc_caches_dma[KMALLOC_SHIFT_HIGH + 1];
-#endif
-
 static int __init setup_slub_min_order(char *str)
 {
 	get_option (&str, &slub_min_order);
@@ -2282,6 +2278,47 @@ panic:
 	panic("Creation of kmalloc slab %s size=%d failed.\n", name, size);
 }
 
+#ifdef CONFIG_ZONE_DMA
+static struct kmem_cache *kmalloc_caches_dma[KMALLOC_SHIFT_HIGH + 1];
+
+static noinline struct kmem_cache *dma_kmalloc_cache(int index, gfp_t flags)
+{
+	struct kmem_cache *s;
+	struct kmem_cache *x;
+	char *text;
+	size_t realsize;
+
+	s = kmalloc_caches_dma[index];
+	if (s)
+		return s;
+
+	/* Dynamically create dma cache */
+	x = kmalloc(kmem_size, flags & ~SLUB_DMA);
+	if (!x)
+		panic("Unable to allocate memory for dma cache\n");
+
+	if (index <= KMALLOC_SHIFT_HIGH)
+		realsize = 1 << index;
+	else {
+		if (index == 1)
+			realsize = 96;
+		else
+			realsize = 192;
+	}
+
+	text = kasprintf(flags & ~SLUB_DMA, "kmalloc_dma-%d",
+			(unsigned int)realsize);
+	s = create_kmalloc_cache(x, text, realsize, flags);
+	kmalloc_caches_dma[index] = s;
+	return s;
+}
+#else
+static inline struct kmem_cache *dma_kmalloc_cache(int index, gfp_t flags)
+{
+	return NULL;
+}
+#endif
+
 static struct kmem_cache *get_slab(size_t size, gfp_t flags)
 {
 	int index = kmalloc_index(size);
@@ -2293,38 +2330,9 @@ static struct kmem_cache *get_slab(size_
 	if (index < 0)
 		return NULL;
 
-#ifdef CONFIG_ZONE_DMA
-	if ((flags & SLUB_DMA)) {
-		struct kmem_cache *s;
-		struct kmem_cache *x;
-		char *text;
-		size_t realsize;
-
-		s = kmalloc_caches_dma[index];
-		if (s)
-			return s;
-
-		/* Dynamically create dma cache */
-		x = kmalloc(kmem_size, flags & ~SLUB_DMA);
-		if (!x)
-			panic("Unable to allocate memory for dma cache\n");
-
-		if (index <= KMALLOC_SHIFT_HIGH)
-			realsize = 1 << index;
-		else {
-			if (index == 1)
-				realsize = 96;
-			else
-				realsize = 192;
-		}
+	if ((flags & SLUB_DMA))
+		return dma_kmalloc_cache(index, flags);
 
-		text = kasprintf(flags & ~SLUB_DMA, "kmalloc_dma-%d",
-				(unsigned int)realsize);
-		s = create_kmalloc_cache(x, text, realsize, flags);
-		kmalloc_caches_dma[index] = s;
-		return s;
-	}
-#endif
 	return &kmalloc_caches[index];
 }